This invention relates to a directional pneumatic agricultural tire for use on farm tractors and similar agricultural type vehicles.
Tractor tires must have good vibration characteristics on and off the road while maintaining good traction or draw bar characteristics. Such tires must also provide for the removal of soil, mud, etc., during infield use.
The tractive power propelling the vehicle is primarily provided through and transmitted by large lugs that are typically oriented in a directional pattern. This directional pattern generally employs the use of what is commonly called or referred to as long bars or a combination of long bars and short bars. Typically, these patterns of lugs are designed to have two rows of shoulder lugs, one row extending from each shoulder of the tire towards the equatorial plane. The volumetric space between the lugs is commonly referred to as the soil discharge channels. These channels provide a means for compacted soil to discharge over the tire shoulder. This feature prevents the tire from packing with mud and enables the tire to maintain a self-cleaning capability. Generally, these tires having two rows of shoulder lugs are arranged such that the lugs create a V or chevron-type pattern, these patterns usually are centered about the equatorial plane. If they are not centered they are typically alternating such that the chevron is on one side of the equatorial plane and the next set of circumferentially adjacent lugs have a chevron which is on the opposite side of the equatorial plane. This alternating pattern is repeated such that there is a balancing effect of the chevrons. For the purposes of this invention, these alternating chevrons on one side or the other of the equatorial plane in a repeating fashion are considered symmetrical in that as the tire passes through its footprint, that is the portion of the tire contacting the ground surface, the soil discharge channels within the footprint typically average out such that the average volume within the channel is equal on the left side of the equatorial plane versus the right side of the equatorial plane. Such a tire demonstrating a long bar/short bar combination is exhibited in U.S. Pat. No. 4,383,567 and is commonly referred to in the commercial market place as the Goodyear DynaTorque II radial tire.
Another tire using a similar long bar/short bar combination is taught in U.S. Pat. No. 4,534,392. This tire is commonly referred to as the Goodyear DynaTorque Radial and the Kelly-Springfield PowerMac L/S Radial Tractor Tire. This particular tire used a combination of two long bars separated by a short bar and repeated by two long bars and this pattern is repeated on both sides of the tire. This tread pattern is such that it again exhibits a combination of chevrons that have a resultant pattern such that the soil discharge channels as the tire passes through the footprint tend to equalize.
The prior art tires typically had several characteristics in common. One being the employment of a large number of lugs where at least one of the lugs would always cross the centerline of the tire. These tires had several beneficial tractive performance characteristics in that they were good in most soil conditions and provided good draw bar traction. The problem that was prevalent in these types of designs is that the short bar would tend to wear out more rapidly than the long bars. The resultant effect is that an uneven wear pattern would be generated in the tire after a period of time. This meant that the farmer would perceive the tire as being irregularly worn and therefore he considered the employment of a short bar detrimental to the performance of the product.
In 1992, The Goodyear Tire and Rubber Company introduced a new tractor tire having two sets of primary and secondary lugs. The tire was commercially identified as a DT710 and is described in U.S. Pat. No. 5,046,541. As described in the patent, this tire has good traction, vibration and cleaning characteristics. These primary and secondary lugs are shorter in length than most tractor tire lugs. The tire effectively increased the number of lugs and therefore an increase in lug surface area resulted. This increased the performance capabilities of the tire. The flexible nature of these relatively short lugs also helped reduce the soil compaction potential of the tire even though more lug surface area was employed.
In 1995, U.S. Pat. No. 5,411,067 taught that the tire described above as U.S. Pat. No. 4,534,392 the Goodyear DynaTorque Radial and Kelly-Springfield PowerMac L/S Radial Tractor tires could be modified by the employment of a notch in at least each of the long bars across the equatorial plane. This notch could be of partial or full depth. By notching the long bar the tire achieved increased flexibility and reduced soil compaction while further enhancing the tractive capability of the tire. This pattern had the resultant effect of the directional symmetrical patterned tires in that the soil discharge channels throughout the footprint on average from left side to right side were equal as the tire rolled through the soil.
Each of the tires described above had several key limitations; one being that the employment of short lugs in combination with long bar lugs inherently results in a potential nonuniform treadwear problem. Alternatively, the employment of short lugs such as the DT710 although resulting in very uniform wear has bars that are substantially shorter than the typical lugs and as a result the tread although wearing uniformly is perceived by the farmer to have the potential of wearing out quickly because the lugs are substantially shorter than the conventional lugs. This in spite of the fact that there is a larger surface area in the use of the D1710 type short lugs with the resultant effect of more lug surfacing contact as the tire rolls therefore enhancing the wear and durability of this particular tire. Nevertheless, the customer perceives the potential for fast wear due to the use of short lugs.
A tractor of the present invention (10) has a drive axle having mounted thereto a pair of pneumatic agricultural tires 20A, 20B, each having an asymmetric directional tread pattern.
The tire has the unique asymmetric directional tread pattern such that the soil discharge channels between the lugs on one side of the tire are uniformly greater than the soil discharge channels created on the opposite side of the tire. This creates a unique asymmetric soil discharge channel. Additionally, the inventive tire has two rows of shoulder lugs, the lugs being of substantially equal lengths which enables the tire to exhibit very uniform wear patterns.
A pneumatic agricultural tire 20 having a maximum section width (SW), an axis of rotation (R), an equatorial plane (EP) centered between the maximum section width (SW) and perpendicular to the axis (R) is described. The tire 20 has a casing having a carcass 21 having one or more plies 22 reinforced with rubber coated cords 22A and has a rubber tread 32 disposed radially outwardly of the casing. The tread 32 has first and second lateral tread edges 32A,33B; the distance between the lateral tread edges 33A,33B defines the tread width (TW). The tread 32 has an inner tread 34 and a plurality of lugs 50A,50B,50C projecting radially outwardly from the inner tread 34. The tread lugs 50A,50B and 50C have a length ll, and a width lw the ratio of the lug length ll to lug width lw is at least three times, preferably at least three times.
The tread 32 has a plurality of shoulder lugs 50A and 50B. The plurality of shoulder lugs 50A,50B are divided into a first row of shoulder lugs 50A extending from the first lateral edge 33A respectively towards the equatorial plane and a second row of shoulder lugs SOB extending from the second lateral edge 33B. The lugs 50A of the first row are circumferentially offset relative to the lugs 50B of the second row. A plurality of similarly oriented central lugs 50C are arranged in row and each central lug 50C extends across the equatorial plane EP. The lugs of the first row of shoulder lugs 50A are substantially aligned with the central lugs 50C along their respective lug lengths ll, while the shoulder lugs 50B of the second row are similar but oppositely oriented relative to the first row of shoulder lugs 50A. The combination of shoulder lugs 50A,50B and central rugs 50C form an asymmetric chevron pattern 70,72 having a point 74 of the chevron 70,72 located between the equatorial plane EP and the second lateral edge 33B. A primary leg 76 of the chevron 70,72 lies along the substantially aligned lengths of the shoulder lugs 50A of the first row and the central lugs 50C. A secondary leg 78 of the chevron 70,72 lies along the length of the shoulder lugs 50B of the second row and the point 74 of the chevron 70,72.
In the preferred embodiment each of the shoulder lugs 50A of the first row are similar in shape and length. Similarly, each of the shoulder lugs 50B of the second row are of similar shape and length. It is most preferred that both the shoulder lugs 50A and 50B of the first and the second row are of similar shape and length. This is believed to improve the uniform wear of this tread pattern.
It is believed preferable that the circumferentially adjacent chevrons 70,72 have a circumferential overlap (O) as measured by axially extending lines 84,86, the overlapping (O) distance between these lines 84,86 at the extremes of the circumferential overlap being at least 25% of the total circumferential extent (T) of a chevron 70,72 enables the tire 20 to achieve extremely uniform ride and handling characteristics. The shoulder lugs 50A,50B each have an axially outer end 53 and an axially inner end 51. The axially outer ends 53 of the shoulder lugs 50A of the first row are circumferentially offset relative to the axially outer ends 53 of the shoulder lugs 50B of the second row as measured as the distance X circumferentially between axial lines 90,92 tangent to the extremes of the axially outer ends 53. The circumferential offset distance X is at least 75% of the circumferential distance between the axially inner 51 and axially outer ends 53 of the shoulder lugs 50A of the first row. In a preferred embodiment of the tire 20, the tire 20 has a net gross ratio as measured around the entire circumference of the tire of less than 35%, preferably about 22%.
In order to maintain this open tread pattern, each tread lug 50A,50B,50C is spaced a minimum distance(s) of 1.5 the lug width (lw) from an adjacent lug 50A,50B, or 50C. The central lugs are spaced a minimum distance of 1.5 times the central lug width from an adjacent central lug such that the central lugs do not overlap in the circumferential direction.